The present invention relates to an intramedullary support strut for long bones, in particular such a support strut that is expandable from a compact configuration to an extended configuration such as to enable the strut to be inserted into the medullary canal of long bones via a relatively small lateral portal made on the side of the bone.
Diaphyseal fractures of long bones such as the humerus, femur and tibia usually require surgical fixation. Current solutions for such fractures include external fixation and internal fixation. Internal fixation can be divided further into extramnedullary fixation (plate and screws) and the more popular intramedullary fixation. Intrarnedulary fixation consists of nails, which can be classified into flexible, rigid, interlocking and non-interlocking. Interlocking nails are fixed at their ends by screws perpendicular to the axis of the nail, through separate incisions and bony windows or portals. The current popular solutions for isolated subtrochanteric fractures or combined intertrochanteric/subcapital and subtrochanteric fractures consist of compression screw/nail-plate systems with long side plate or intramedullary interlocking nail combined with screw extension into the femoral neck and head. The current solutions for two and three-part proximal humeral fractures (mainly subcapital fractures) include fixation with wires, nails, plates, screws, intramedullary rods, and combinations of the above.
The above solutions have several limitations. For example, in diaphyseal fractures, the plating requires a large skin incision, extensive soft tissue exposure, and stripping of the bone. Intramedullary nailing requires an extensive surgical approach and exposure at the entry site with some bones, and poses risk to important neurovascular structures in others. In isolated proximal femoral fractures and combined intertrochanteric/subtrochanteric femoral fractures, both the screw/plate system and intramedullary nail/screw system require extensive surgical approaches and multiple apertures in the bone. Complications of nail/screw-plate system when applied to the combined fractures are more common than when applied to isolated inter/subtrochanteric fractures, and include loosening of plate screws, failure of plate or plate screw, and higher rates of infection. Regarding proximal humeral fractures, all of the above mentioned techniques fail to demonstrate a consistently stable fixation and a good solution for these fractures is currently lacking.
As it is well established that intramedullary anchoring of fracture fixation devices (screw/nail) in the proximal femur is biomechanically superior to side-plate anchoring of these devices, intramedullary anchoring has become the method of choice for fixation of the more problematic subtrochanteric and combined inter/subtrochantenc fractures. For isolated intertrochantenc fractures, the side plate anchoring system is still the method of choice. This is because of the extensive surgical approach and multiple bony entry points involved with the currently available combination screw-intramedullary nail systems is deemed unjustifiable. However, the combination of a solution that provides both the biomechanical stability of intramedullarv fixation and a minimally invasive surgical approach, would appear to be particularly advantageous.
All currently used techniques for reducing and fixating subcapital humeral fractures have ultimately proven to be unsatisfactory in one way or another. Therefore, any solution to these problematic fractures that would consistently demonstrate satisfactory results would constitute an improvement.
WO 95 22292 discloses a tissue lengthening device for lengthening a bone, and is not concerned with providing mechanical support for the bone. In this reference, both the distal and proximal portions of the device are fully anchored in the bone before any relative movement commences between the two portions of the device. Thus, this is the xe2x80x9cretractedxe2x80x9d configuration of this device, which has to be inserted into the long bone via a superior portal made in the bone. The device cannot be introduced into the medullary canal via a transverse portal made in the bone, since such a portal would have to comprise the length of the device, i.e., approximately the longitudinal length of the bone, which would be needlessly destructive to the bone and surrounding tissues. Further, the device does not extend into the bone, but remains where it is relative to the medullary canal, and instead lengthens the bone slowly, in registry with the extension of the device itself.
U.S. Pat. No. 4,190,044 is directed to an intermedullary pin for the repair of a bone. The pin has two sections, an inner section of which is retracted into the other outer section. The pin is inserted into one of the two broken bone fragments via a medullary opening at the break, and then the two halves of the bones are aligned together. Thereafter, by means of a wire, the inner section of the pin is extended into the medullary canal of the second bone fragment, again via the break. Thus, the pin, in its xe2x80x9cretractedxe2x80x9d configuration, must be long enough to be well-anchored into the bone fragment, and moreover it is inserted therein longitudinally via the break in the fragment, rather than through a lateral portal, since the break in the bone already provides a portal for the pin.
U.S. Pat. No. 4,936,856 deals with an acetabular prosthesis to be supported in a cavity in the hip bone. The prosthesis comprises a socket member adapted for being anchored to the bone, and at least one elongated support adapted to be coupled with the socket member and configured to extend outwardly a variable length from the outer surface of the socket into the cavity. In one embodiment, the elongated support is in the form of a telescopically constructed support, wherein smallest diameter sleeve is extended outwardly from the socket until it reaches the bone in the cavity. The xe2x80x9ctelescopic constructed supportxe2x80x9d is but one manner proposed in this reference for providing a longitudinal support that extends from the socket to the bone within the cavity, and this xe2x80x9ctelescopic constructed supportxe2x80x9d is in any case provided on the socket via a longitudinal bore therein. The criterion defining the xe2x80x9cretractedxe2x80x9d configuration of the xe2x80x9ctelescopic constructed supportxe2x80x9d is that the longitudinal length of each element should not exceed that of the bore. There is no disclosure or suggestion of a support strut at all, less so with the characterizing feature of the present invention.
It is an aim of the present invention to provide a fixation device for accommodation in the medullary canal that overcomes the limitations of prior art devices.
It is another aim of the present invention to provide an intra-medullary support strut for long bones that has a variety of applications.
It is another aim of the present invention to provide a stem for a femoral head prosthesis or a humeral head prosthesis requiring a minimally invasive surgical approach for its implantation relative to currently used extensive methods of surgery.
It is another aim of the present invention to provide a stem for a femoral or humeral head prosthesis having a rigidity closer to that of bone thus reducing stress shielding encountered in currently available prostheses.
It is another aim of the present invention to provide a stem/anchor for screw/nail fixation devices of isolated and combined proximal femoral fractures, offering a more stable biomechanical fixation than side plate fixation of these devices.
It is another aim of the present invention to provide a stem/anchor for screw/nail fixation devices of isolated and combined proximal femoral fractures such that permit a minimal surgical approach.
It is another aim of the present invention to provide a fixation device for diaphyseal fractures in long bones requiring a less extensive surgical approach.
It is another aim of the present invention to provide a fixation device for proximal humeral fractures offering a stable fixation where no one universally accepted and consistently satisfactory solution exists.
The present invention relates to an intrarmedullary support strut for long bones comprising at least two telescopic members adapted for longitudinal displacement relative to each other from a retracted configuration of said strut having a first longitudinal length to an extended configuration of said strut having a second longitudinal length, wherein said strut is adapted in said extended configuration for accommodation in a longitudinal cavity formed in the medullary canal of said long bone and for providing therein a mechanical support structure for said long bone, and wherein said strut comprises in said retracted configuration a transverse profile adapted for enabling said strut to be inserted into said long bone via a suitable lateral portal formed through the lateral cortex of the long bone, such as to enable said strut to be aligned with and extended into said cavity.
Preferably, a most proximally disposed said telescopic member constitutes a base member adapted for remaining within said portal when said strut is in extended configuration. Optionally, said strut comprises a cap portion at the distal end of the innermost said telescopic member.
The ratio of the diameter of said strut to said first length is typically between about 0.5 and about 2.0, and preferably about 1.25, and the ratio of said second length to said first length is typically between about 3 and about 10, and preferably about 8. Typically, said strut comprises between 3 and 10, and preferably 8 said telescopic members.
Optionally, said telescopic members are adapted for sliding longitudinal displacement relative to each other from said retracted to said extended configuration. Alternatively, said telescopic members are adapted for longitudinal displacement relative to each other from said retracted configuration to said extended configuration by each said telescopic member having at least a portion of the inside surfaces thereof screw-threaded and at least a portion of their outside surfaces complimentary threaded to engage with the inside surface of the externally-adjacent telescopic member.
Optionally, each said telescopic member comprises a substantially circular, elliptical, triangular, rectangular or polygonal longitudinal cross-sectional profile. The lateral portal may be disposed at an angle between about 90xc2x0 and about 150xc2x0 to said longitudinal cavity.
Optionally, said intramedullary support strut further comprises actuating means for extending said strut from said retracted configuration to said extended configuration. The actuating means may comprise a liquid injected under pressure into said strut via a suitable openimg therein, or alternatively an inflatable bag in said strut and in communication with said opening for receiving said liquid and for preventing leakage of liquid therefrom, or alternatively a feeding wire arrangement comprising a wire having a distal end attached to the distal end of said innermost telescopic member, and a wire feeder for feeding said wire distally with respect to said base member. Such a feeding wire may be disposed external to said strut, or alternatively, the feeding wire is disposed internally in said strut, wherein said wire feeder comprises a spool for feeding said wire to said strut, said spool being operatively connected to a motor means.
Alternatively, the actuating means may comprise a suitable reamer having a suitable reamer head at one end thereof rotatably mounted, preferably permanently, with respect to an innermost telescopic member, wherein rotation of said reamer head and advancement thereof in a distal direction by suitable rotation means automatically opens the said strut. Preferably, said rotation means comprises a suitable power tool. Optionally, the reamer comprises a flexible reamer driveshaft removably connected to the said reamer head at one thereof, and to said power tool at the other end thereof. The reaming diameter of said reamer head may be at least equal to or greater than the diameter of said base member.
Alternatively, wherein said actuating means comprises a suitable reamer having a suitable reamer head at one end thereof releasably rotatably engageable with respect to an innermost telescopic member, wherein rotation of said reamer head and advancement thereof in a distal direction by suitable rotation means automatically opens the said strut. The reaming diameter of said reamer head is typically smaller than the diameter of said innermost telescopic member.
Said support strut optionally further comprises locking means for maintaining said strut in said extended configuration. The locking means may comprise suitable stops between adjacent said telescopic members adapted to prevent relative movement therebetween when said strut is in said extended configuration. Alternatively, the locking means may comprise an inflatable bag having an opening for receiving a suitable liquid, said bag adapted for maintaining said liquid at a suitable pressure. Altematively, the locking means comprises at least one semi-rigid bar insertable within said strut when said strut is in said extended configuration. Alternatively, the locking means comprises a screw or nail for locking the said innermost telescopic member with respect to said long bone, when said strut is in said extended configuration. Alternatively, the locking means comprises suitable bone cement provided between said strut and said cavity when said strut is in said extended configuration. Alternatively, the locking means comprises a suitable flowable polymer injected into said strut when said strut is in said extended configuration, said flowable polymer being adapted for setting and hardening in situ. Such a flowable polymer may be one of PMMA or Silastic.
Alternatively, each said telescopic member is formed as a frustro-conical unit, having the inside surfaces thereof screw-threaded and the distal parts of their outside surfaces threaded to engage with the inside surface of the externally-adjacent telescopic member, wherein to provide said locking means.
The intramedullary support strut may be adapted for anchoring a hip or shoulder hemi/total arthroplasty prosthesis.
Alternatively, the intramedullary support strut may be adapted for the intramedutlary fixation of diaphyseal fractures of long bones.
Alternatively, the intramedullary support strut may be adapted for the intramedullary fixation or anchoring of compression screw fixation system for isolated intertrochanteric and subtrochanteric fractures.
Alternatively, the intramedullary support strut may be adapted for the intramedullary fixation or anchoring of compression screw fixation system for combined intertrochanteric/subcapital femoral fractures with subtrochanteric fractures.
Alternatively, the intramedullary support strut may be adapted for the intramedullary fixation or anchoring of compression screw fixation system for subcapital or proximal humeral fractures not requiring arthroplasty.